1. Field of the Invention
In a small scale computer system, a disk storage which uses a recording medium called a floppy disk is connected as a file storage. The present invention relates to a controller for controlling an operation of such a disk storage.
2. Description of the Prior Art
In the floppy disk storage, each track of the disk is usually divided into a plurality of areas of equal and phyically fixed length, and data is read and written by the area as a unit. This area is called a sector and a maximum number of bytes stored in the sector is called a sector length.
In the past, a single density recording system in which 128 bytes of data are stored in one sector has been widely used, but in recent years, a double density recording system in which the recording density is doubled and the sector length is increased to 256, 512 or 1024 bytes has been used. Accordingly, it is necessary that the floppy disk storage be compatible with various types of floppy disks.
When data is read from or written into the floppy disk, it is necessary, as a matter of course, to prepare a reference signal which matches the recording density of the floppy disk used. Furthermore, the data cannot be read or written without the knowledge of the sector length of the floppy disk used. Thus, when a floppy disk storage to which various floppy disks of different recording densities and different sector lengths may be loaded is to be accessed, information for specifying the recording density and the sector length (hereinafter referred to as recording status information (RSI) is necessary in addition to address information.
A conventional floppy disk has an index track which was recorded in the single density recording system and includes the RSI of the floppy disk. In the conventional floppy disk storage, the RSI is first read from the index track at the time of first access and it is stored in a memory of a disk controller, and then desired data is accessed. In the subsequent accesses, the RSI of the floppy disk is read from the memory and then desired data is accessed. However, in such a system, since the RSI has to be first read from the index track at the first access, an extra access time is required and the overall access time increases.